Answer
8.1%
Work Step by Step
Mass fraction calculated first
$w_{a}$=$\frac{C_{g}-C_{0}}{C_{g}-C_{a}}$=$\frac{10-2.5}{100-0}$=0.97
$w_{g}$=$\frac{C_{0}-C_{a}}{C_{g}-C_{a}}$=$\frac{2.5-0}{100-0}$=0.025
now mass fraction can be converted into volume fraction
$V$=$\frac{\frac{w_{g}}{d_{g}}}{\frac{w_{a}}{d_{a}}-\frac{w_{g}}{d_{g}}}$ $\times100$ =$\frac{\frac{0.025}{2.3}}{\frac{0.97}{7.9}+\frac{0.025}{2.3}}$ $\times100$ =8.1%
